Speed detecting apparatus for a rotatable loud-speaker



Nov. 17, 1970 SHINICHI MURAKAMI 3,541,369

SPEED DETECTING APPARATUS FOR A ROTATABLE LOUD-SPEAKER Filed March 13, 1969 2 Sheets-$heet 1 F I I 15 CONVERTER A4 COMPARATQR AMP.

REFERENCE VOLTAGE SOURCE 18 S POWER SUPPLY I N VEN TOR 511mm Hl/PIKAM/ 5 BY I Nov. 17, 11970 SHlNlCHl MURAKAMI 3,541,369

SPEED DETECTING APPARATUS FOR A ROTATABLE LOUD-SPEAKER Filed March13, 1969 Z-Sheets-Sheet 2 United States Patent O US. Cl. 310-168 Claims ABSTRACT OF THE DISCLOSURE A speed detecting apparatus for a rotatable loudspeaker comprises a wheel made of non-magnetic ma terial and fitted to the shaft of a motor driving another shaft, to which is attached a rotatable loud-speaker, and a detecting element disposed adjacent to the periphery of said wheel. The clearance between the detecting element and the wheel periphery is adjustable.

The wheel comprises a speed detecting section formed of a plurality of permanent magnets embedded in the peripheral portion thereof and used in speed detection jointly with the detecting element, and is formed integrally with a motor pulley in adjacent relationship along the motor shaft, said motor pulley having a belt stretched across said pulley and another pulley fitted to the rotary shaft to which is attached the rotatable loud-speaker. The wheel can be fitted close to the bearing of the motor rotor and is prevented from detection errors caused by the transverse vibrations of the motor shaft.

BACKGROUND OF THE INVENTION The present invention relates to a speed detecting apparatus, and more particularly to improvements in a speed detecting apparatus for a rotatable loud-speaker, which is used in detecting the voltage of electrical signals corresponding to the rotation speed of the loud-speaker when it is rotated to vary the direction in which sounds are radially sent forth therefrom so as to furnish a tremulant effect to the tones of an electronic musical instrument.

Where it is desired to furnish the tones given by an electronic musical instrument with a tremulant effect, the method used is either to subject the prescribed frequency of musical tone signals to amplitude modulation or rotate a loud-speaker sending forth musical tones in a manner to cause said tones to be radiated in a direction perpendicular to the axis of rotation and periodically change the amplitude of musical tone signals.

With an electronic musical instrument using the prior art rotatable loudspeaker to produce tremulant tones, the loud-speaker is mechanically connected to a motor and rotated at a speed determined jointly by the prescribed rotating speed of a motor and the ratio in which the rotating moment of the motor is transmitted to the speaker by a rotating moment transmitting mechanism. In other words, the rotating speed of the rotatable loudspeaker, namely, the speed of reiterated tremulant cycles furnished to musical tone signals is limited by the prescribed rotating speed of the motor and the mechanism for transmitting the rotating moment of the motor.

The means heretofore proposed to obtain a varied tremulant effect by changing the rotating speed of the loud-speaker consists in, for example, providing a plurality of motors having different rotating speeds as a source of motive power and alternately using, as occasion demands, such motors having different rotating speeds or varying the ratio in which the aforesaid transmitting mechanism conveys the rotating moment to the rotatable loud-speaker by means of a mechanical switchover device. However, these means can change the rotating speed of the loud-speaker only stepwise and also fails to vary said speed over a fully broad range.

Accordingly, such kind of rotatable loud-speaker was desired to be capable of varying its rotating speed over a broad range and there has already been proposed a de vice shown in FIG. 1, for example. There will now be described the operation of this device. The rotating speed of a motor 11 to rotate a loud-speaker 12 is detected by a speed detector 13, obtaining electrical signals corresponding to the rotating speed of the motor. The detected electrical signals are converted by a voltage conversion circuit 14 to voltage signals proportionate to the rotating speed of the motor 11.

The voltage of said signals is compared by a comparator 15 with the reference voltage supplied by a reference voltage source 16 for setting the motor speed. This reference voltage source 16 is intended to obtain a voltage corresponding to the desired rotating speed of the motor 11, namely, the speed of reiterated tremulant cycles which is desired to be obtained, for example, by means of a variable resistor.

Thus, electrical signals representing the difference between the aforementioned voltages which are led out of the comparator 15 indicate the difference between the speed of tremulant cycles specified at that time and the rotating speed of the loudspeaker 12.

Output signals from the comparator 15 corresponding to said voltage difference are amplified by an amplifier 17 and supplied to a regulator 18. This regulator varies the rotating speed of the motor 11 by regulating the voltage fed to the motor 11 from a power supply 19 to reduce the voltage difference to zero.

With a detecting device of the aforementioned arrangement, it is necessary to detect the rotating speed of a motor or a loud-speaker driven jointly therewith in the form of electrical signals having a voltage corresponding to the rotating speed. The means of detecting the rotating speed and converting it to electrical signals having a voltage corresponding to said rotating speed generally comprises a generator used in interlocking relationship with the rotary shaft of a rotatable loud-speaker. However, employment of such a generator renders at detecting device remarkably complicated and expensive and is practically unsuitable for an electronic musical instrument of which Said device constitutes a very fractional part.

SUMMARY OF THE INVENTION It is accordingly the main object of the present invention to provide a speed detecting apparatus for a rotatable loud-speaker which can detect the rotating speed of a motor or a rotatable loud-speaker driven jointly therewith by a fully simple and compact arrangement, and without using a generator and subjecting the motor to a heavy load and is well adapted for incorporation in an electronic musical instrument.

Another object of the present invention is to provide a speed detecting apparatus for a rotatable loud-speaker which can always detect the rotating speed of a rotatable loud-speaker unfailingly and accurately.

Still another object of the present invention is to provide a speed detecting apparatus for a rotatable loudspeaker which enables the clearance between the detecting element and wheel constituting said apparatus to be easily and properly adjusted for accurate determination of speed signals.

A speed detecting apparatus of the present invention for a rotatable loud-speaker comprises a wheel made of non-magnetic material fitted to the shaft of a motor driving another shaft to which is attached the rotatable loudspeaker, and a detecting element disposed adjacent to the periphery of the wheel. The wheel comprises a speed detecting section having a plurality of permanent magnets embedded in the periphery of the wheel and used in speed detection jointly with the detecting element and is formed integrally with a motor pulley in adjacent relationship along the motor shaft, said motor pulley having a belt stretched across said pulley and another pulley fitted to the rotary shaft to which is attached the rotatable loudspeaker. Further provided is means for adjusting the clearance between the detecting element and the magnets.

The wheel can be fitted close to the bearing of the motor rotor and is prevented from detection errors resulting from the transverse vibrations of the motor shaft. Accordingly, the speed detecting apparatus of the present invention can perform speed detection with great accuracy by means of a simple arrangement.

BRIEF EXPLANATION OF THE DRAWINGS Other and further objects and advantages of the present invention will be apparent from the following description when taken in connection with the accompanying drawings, wherein:

FIG. 1 shows a speed control circuit diagram for a rotatable loud-speaker;

FIG. 2 is a side view of a speed detecting apparatus for a rotatable loud-speaker according to an embodiment of the present invention;

FIG. 3 is an elevation of a wheel used in said embodi ment;

FIG. 4 is a side view, with part broken away, of the wheel of FIG. 3; and

FIG. 5 is a fragmentary perspective view showing a rotatable loud-speaker,

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS There will now be described an embodiment of the present invention by reference to FIGS. 2 to 5. Referring to FIG. 2, numeral 21 denotes a wall member forming the cabinet of an electronic musical instrument, for example. The wall member 21 has an L-shaped fitting plate 22 attached thereto by the medium of bushings 23 and 24. On that portion of the L-shaped fitting plate 22 which is perpendicular to the wall member 21 is mounted a support plate 25 by means of bushings 26 and 27. To the support plate 25 is integrally attached a motor supporting plate 28 in perpendicular relationship thereto.

On the motor supporting plate 28 is mounted a motor 48 having a rotor bearing (not shown) supporting a motor shaft 29 in a manner to allow it to rotate therethrough. A wheel 32 is fitted by screws 30 and 31 to that portion of the motor shaft 29 extending through the rotor bearing, in adjacent relationship to said rotor bearing of the motor, whereby the wheel 32 is rotatable with the rotation of the motor shaft 29.

The wheel 32 is made of non-magnetic material such as synthetic resin, and is provided, as shown in FIGS. 3 and 4, with a plurality of, for example, six equally spaced notches formed on the periphery. In these notches are embedded permanent magnets such as rubber magnets 33 to 38 thereby to form the speed detecting section 39 of the wheel 32. Adjacent to this speed detecting section 39 is integrally formed a motor pulley 40 over which is stretched a belt 41. It will be apparent that the speed detecting section 39 may be formed by fitting an annular multi-pole magnet to the periphery of the wheel 32.

The belt 41 stretched over the sleeve of the motor pulley 40 extends, as shown in FIG. 5, to a pulley 49 fitted to a rotary shaft to which is attached a rotatable loudspeaker 51. The loud-speaker 51 is disposed on the rotary shaft 50 in such a manner that sounds are radiated from it in a direction substantially perpendicular to the rotary shaft, and is thus made to rotate in corresponding relationship to the rotating speed of the motor. The musical tones t are sent forth from the loud-speaker in a state modified by a tremulant effect as a result of its rotation.

The wheel 32 of the aforementioned arrangement is used in speed detection jointly with a detecting element 42. The support plate 25 has an extension strip 43 integrally formed therewith which spatially faces the wheel 32 in parallel relationship to the tangential line of the periphery of said wheel 32. The extension strip 43 may be formed by cutting and bending part of the support plate 25 or it is possible to attach a separately prepared strip to said plate 25. On that side of the extension strip 43 facing the wheel 32 is disposed a plate spring 44 with one of its ends fixed to the extension strip 43. The other end of the plate spring 44 is so bent as spatially to face the extension strip 43. To that side of said other end of the plate spring 44 facing the wheel 32 is fixed a horseshoe core 45 with its open end directed toward the wheel 32. Around one of the legs of the horseshoe core 45 is wound an induction detection coil 46. Through a hole perforated in the extension strip 43 is inserted an adjusting screw 47 so as to cause one of its ends to contact the aforesaid other end of the plate spring 44. The clearance between the detecting element 42 and the periphery of the wheel 32 is rendered variable by the forward and backward rotation of the adjusting screw 47.

In this case, the speed detecting section 39 and the detecting element 42 may be positioned in spaced relationship from each other either in the axial or radial direction of the wheel 32. But it is more preferable that they are positioned spatially in the radial direction of the wheel 32, because the clearance between the detecting element 42 and the rotating wheel 32 is less liable to change, enabling speed detection to be performed with greater accuracy.

According to the rotating speed detecting apparatus of the present invention arranged as described above, the rotation of the wheel 32 allows the permanent magnets 33 to 38 positioned on the periphery of the wheel 32 to pass near the induction detecting coil 46. When the permanent magnets 33 to 38 pass by, there are induced in the detection coil 46 pulse signals having an amplitude and frequency corresponding to the rotating speed of the wheel 32, namely, the speed and frequency at which the permanent magnets 33 to 38 pass before the detection coil 46. Accordingly, the pulse frequency of voltage signals thus obtained or an integrated value thereof directly represent the rotating speed of the wheel 32. Therefore, the speed detecting apparatus of the present invention can be effectively used as such in the speed control circuit for a loudspeaker as shown in FIG. 1.

In this case, the sensitivity with which the induction detection coil 46 detects rotation speed is affected by the magnitude of the clearance between said coil 46 and the periphery of the wheel 32. However, this clearance can be controlled by the adjusting screw 47 to a most suitable value, normally 2 to 3 mm., enabling the detection of rotation speed to be always carried out under a stable condition.

Further according to the present invention, the wheel 32 and pulley member 40 thereof are integrally formed in adjacent relationship and also positioned as close as possible to the rotor bearing of the motor 48 by means of fitting screws 30 and 31. Consequently variations in the clearance between the induction detection coil 46 and wheel 32 resulting from the transverse vibrations of the motor shaft 29 caused by the shaking of the belt 41 are deemed substantially negligible, enabling detection of the rotating speed to be carried out under a stable condition. Further, the shaking of the belt 41 or other external impacts may sometimes cause the entire parts fitted to the bushings 26 and 27 to quake. However, since the wheel 32 and detection coil 46 are securely fixed on the support plate 25, such quaking will not have any harmful effect on the accuracy of detection.

The foregoing embodiment relates to the case where sounds are radiated from the loud-speaker in a direction perpendicular to the axis of the rotation. However, it is possible to select any other desired direction in which the radiation of sounds defines different angles from right angles with the axis of said rotation.

Further, the direction of sound radiation may be aligned with the rotating axis of the loud-speaker. At this time, sounds from the loud-speaker assume the form of vibratos and not tremolos. However, it will be apparent that this case is also included in the scope of the present invention.

Further according to the aforementioned embodiment, the rotatingmoment of the motor is transmitted to the rotary shaft 50 by the medium of the belt 41 So as to rotate the loud-speaker 51. However, it is of course possible to cause the motor shaft 29 to be directly coupled with the rotary shaft of the rotatable loud-speaker.

In the embodiments shown above, it is found desirable, according to the inventors experiments, that the diameter of the wheel, namely, that of the rotating locus of the outermost side of the permanent magnets embedded in the periphery of the wheel be made equal to the diameter of the motor rotor and that the detection coil be positioned at the magnetic shield cover of the motor, since the magnets on the periphery of the wheel and detection coil are not subject to any unfavorable effects resulting from induction by the motor or leakage field.

What is claimed is:

1. A speed detecting apparatus for a motor driven rotatable loud-speaker comprising a wheel made of nonmagnetic material and disposed on the rotary shaft of said motor, said wheel having a plurality of permanent magnets spatially arranged on the periphery thereof to form a speed detecting section; a detecting element having a detection coil; and means for resiliently supporting said coil close to said permanent magnets of the wheel with a clearance therebetween and for adjusting said clearance in a radial direction of said wheel.

2. The speed detecting apparatus according to claim 1 wherein the speed detecting section and the detecting element are positioned in spaced relationship from each other in the radial direction of the wheel.

3. The speed detecting apparatus according to claim 1 wherein said detecting element includes a horseshoe core on which the detection coil is wound, and wherein said resilient supporting means comprises: a support plate disposed adjacent and spaced from the rotating periphery of said wheel; a resilient plate spring spatially located between the wheel and said support plate, one end of said plate spring carrying said horseshoe core and the other end of said plate spring being fixed to said support plate;

toward said speed detecting section, thereby adjusting the clearance between said coil and said magnets.

4. The speed detecting apparatus according to claim 1 comprising notches formed in the periphery of said wheel and said permanent magnets are rubber magnets embedded in said notches.

5. The speed detecting apparatus according to claim 3 comprising notches formed in the periphery of said wheel and said permanent magnets are rubber magnets embedded in said notches.

6. The speed detecting apparatus according to claim 1 wherein the speed detecting section includes an annular rnulti-pole magnetic member.

7. The speed detecting apparatus according to claim 3 wherein the speed detecting section includes an annular multi-pole magnetic member.

8. The speed detecting apparatus according to claim 3 wherein the speed detecting section and the detecting element are positioned in spaced relationship from each other in the radial direction of the wheel.

9. The speed detecting apparatus according to claim 1 comprising a first pulley formed integrally with said wheel and adjacent thereto; a second pulley coupled to the shaft of said motor; and a belt stretched over said first and second pulleys to cause said wheel to rotate in synchronism with said rotatable loud-speaker.

10. The speed detecting apparatus according to claim 3 comprising a first pulley formed integrally with said wheel and adacent thereto; a second pulley coupled to the shaft of said motor; and a belt stretched over said first and second pulleys to cause said wheel to rotate in synchronism with said rotatable loud-speaker.

References Cited UNITED STATES PATENTS 1,301,077 4/1919 Pennington 310-168 2,113,226 4/1938 Young 310-169 2,671,882 13/1954 Page 310-168 2,931,020 3/1960 Bender 340-34 3,132,337 5/1964 Martin 310- 3,134,918 5/1964 Eichenberger 310-168 3,230,407 1/1966 March 310-168 3,267,399 8/1966 Spieker 310-168 3,408,573 10/1968 Wullkopf 335-303 MILTON O. HIRSHFIELD, Primary Examiner R. SKUDY, Assistant Examiner US. Cl. X.R. 310-91 

